This invention relates to improved apparatus for assisting in the process of connecting a length of pipe to the upper end of a drill string. The invention is in some respects especially useful in a top drive drilling arrangement, and will be described primarily as applied to that use, though it will be apparent that some features of the invention may also be applicable to other types of drilling apparatus.
In my copending U.S. patent application Ser. No. 677,988 filed Dec. 4, 1984 on "Top Drive Drilling Systems", I have disclosed methods and apparatus for permitting the drill string of a top drive drilling system to be pulled upwardly off of the bottom of the hole each time that a length of pipe is to be added to the upper end of the string, in order to reduce the possibility that the string may become stuck in the hole, or, in case of an offshore well drilled from a floating vessel, to prevent damage to the string resulting from wave motion. The apparatus of that prior invention includes a back-up tool which is capable of engaging the upper threaded end of the string at an elevated location spaced above the floor of the rig and retaining the string against rotation as a length of pipe is connected threadedly to its upper end. In one form of the invention, the tong is mounted for swinging movement between an active position for engaging and holding the upper end of the string at the elevated location and a laterally retracted position in which the back-up tool remains during drilling.